Sorter conveyors with an endless chain of linked conveyor units each having discharge means driven and controlled from the conveyor unit are well-known in the prior art. The discharge means are powered from the stationary part of the conveyor by means of conductor rails and collector shoes on the moving part of the conveyor, by means of electric generators driven by wheels on the conveyor units running on stationary tracks or by an inductive energy transfer system.
The discharge means are commonly controlled by means of control units on the conveyor units, controlling the discharge means of one or a few adjacent conveyor units. The control signals for controlling discharge of articles or other operations, such as moving of cross-belts during induction of articles, tilt of trays in curves to counteract the apparent centrifugal force or at induction stations to catch articles, etc., are transmitted to the control units by means of stationary data transmission means arranged along the conveying path of the conveyor immediately before each of the discharge stations, induction stations, curves, etc.
The individually controllable discharge means offer many advantages but have also some drawbacks. The plurality of stationary data transmission means require an extensive installation operation including wiring from a central control unit to each of the data transmission means and maintenance and readjustment operation is also labour intensive.
An alternative solution is described in the international patent application WO 96/31381 and the related U.S. Pat. No. 6,089,512 disclosing a conveyor system in which data are transmitted to each transport element via a transmission head that continuously is in data transmission contact with a stationary line or the like disposed along the entire path of the conveyor. This solution has the same drawbacks as the above described system.